Apparatus for controlling work feed rate for cutting wood, metal and other materials

ABSTRACT

A positioned sensing device measures and/or calculates the lateral position and movement of a saw blade. These measured and calculated values are used to automatically alter the work-feed rate and/or saw blade rim speed either up or down as sawing conditions change within the work piece or between different work pieces.

REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of application Ser. No.08/569,518, filed Dec. 8, 1995, Apparatus for Controlling Work Feed Ratefor Cutting Wood, Metal and other Materials. The '518 application havebeen allowed but has not issued. This application is filed pursuant to35 USC §120 and 37 C.F.R. 1.53(b).

DESCRIPTION BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] This invention relates to circular saw and bandsaw machines, andincorporates a method of controlling the rate at which work is fed intothe saw blade based upon performance of the saw blade withinpredetermined levels of stability.

[0004] 2. Background

[0005] Circular saw and bandsaw machines have long been used aseconomical means for cutting wood, metal and other materials. Inrecognition of the high costs for raw material and labor,automatic/computer control of work feed rates and sawing accuracybecomes of paramount importance. Optimized automatic control of workfeed rates and saw blade stability keeps material and production costsdown. The use of thinner saw blades and smaller rough sawn dimensionsizes can conserve natural resources in the wood products industry, andreduce material waste in all industries which use circular saw andbandsaw machines in the manufacturing process. In the lumber industry,current production methods result in a larger than necessary amount ofwaste in order to manufacture finished dimension lumber. Reduction ofthis waste requires the solution of several technical problems.

[0006] The first problem is the rate at which the work is fed into thesaw blade. The work is either manually or automatically fed into thesesawing machines. In manually fed machines, the operator listens to thesound of the saw blade and varies the feed rate by judgment, frequentlynot realizing that the saw blade is being overfed. Sawing machineshaving automatic feed systems, use predetermined feed rates as afunction of thickness of work (depth of cut). These predetermined feedrates do not consider any variable except depth of cut. This automaticfeed system permits overfeeding and in some cases underfeeding of thesaw machine, resulting in erratic lateral movement of the saw blade andloss of control of the saw line. Slower than optimum feed rates arerequired to compensate for the variable densities of wood encounteredfrom summer to winter, density changes within the same log, partiallyfrozen logs, and the sharpness of the saw blade cutting teeth. Thevariables all require on-line adjustments to work feed rates.

[0007] The second problem is the target size of the rough sawn work,which must be maintained large enough so that finished lumber is notundersized. This excess material, which is later removed to producefinish dimension lumber, represents waste. Uncontrolled lateraldeviations in the saw lines during the cutting operation require largerrough sawn target sizes. These saw blade movements have several causes:misalignment of saw blade guides, normal saw blade tooth wear, bendingor uneven dulling of saw teeth, and knots in the saw log. These typicalconditions can cause lateral instability of the saw blade, withresultant deviations of the saw line.

[0008] The third problem is offsetting of the saw blade from the desiredsaw line. If the saw teeth are dulled by sand, gravel or other foreignobjects embedded within the material being cut, offsetting the saw linefrom minor deviation of 0.005 to a major of 0.080 of an inch. When a sawblade runs in an offset condition and encounters a knot, or issubstantially over-fed, it is possible for the saw blade to runcompletely out of the work. This ruins the saw blade tension, requiringhours of bench work to bring the saw back into proper tension so that itwill again cut straight and accurately. The saw blade could alsodisintegrate, destroying itself and surrounding equipment, thusrequiring down time to repair the damage. The safety of personnel isalso placed in jeopardy if the saw blade disintegrates.

[0009] The fourth problem is the width of the saw cut, or kerf.Reduction of the saw blade gauge/thickness, and of side clearance, (thedistance the tooth extends beyond the side of the saw blade body),decreases the width of the kerf. Heavier gauges and larger sideclearance are currently used to protect the saw from the instabilityeffects of excessive feed rates.

[0010] The fifth problem encompasses other considerations that directlyaffect optimized cutting efficiency, such as saw blade design, saw bladestrain, and guide pressure.

[0011] At the present time, these considerations are being addressed byusing larger rough sawn lumber target sizes, thicker saw blades, andlarger kerf dimensions. Numerous attempts through the years have beenmade to solve these problems, with varied success.

[0012] 1. Saw blade strain devices such as weight and lever or highstrain pneumatic systems have improved saw blade performance. Someimprovement in saw blade stability has been obtained, and higher feedrates achieved.

[0013] 2. The use of pressure guides provides an additional increment ofsaw blade stability. These devices are commonly used in the woodproducts industry.

[0014] 3. A control system utilizing the saw blade sagging angle in thedirection of the work feed was the basis for U.S. Pat. No. 4,437,367,which was issued to Karl Hauser. This system works well in small bandsawmachines, but will not function adequately with the larger bandmillmachines which have wider saw blades. This patent applies to bandsawmachines that hinge and move to the work in lieu of the work feed systemcommon in larger sawing machines in which the work is fed into themachine.

[0015] 4. Utilizing the pressure imposed by the work on the back of thesaw blade to control work feed rates, as in U.S. Pat. No. 3,680,417issued to John R. Wells, has merit when using small bandmill machineswhich use throw-away saw blades. Large band saw machines have bladewidths exceeding two inches, and the same problems exist with thispatent as with the saw blade sagging angle control system.

[0016] 5. Utilizing a control system as shown in my U.S. Pat. No.4,644,832, which uses a mean or averaged signal proportional to thelateral position of the saw blade for slowing down the depth of cutentry speed. This patent allows for the work entry feed speeds to be sethigher than normal and the control logic to use “slow down steps” toreduce work feed speed in the event of unacceptable lateral movement ofthe saw blade. However, using this system, once a slow-down step hasbeen made, the speed remains slowed down for the entire length of a logor cant being sawn, which lowers production output. This prior art doesnot address variable conditions within the same work piece, such as alog wherein the sawing conditions may vary significantly from one end toanother, for example, from the butt end to the top end, as they relateto material density, sap rings, moisture content and even temperature.

[0017] In addition, my prior U.S. Pat. No. 4,644,832, does not take intoconsideration changes in zero reference signals which can change, in a2-hour period, as much as 0.020 inches as a result of wear duringcutting.

[0018] Finally, this prior art patent utilizes only processed signals,and in the event of significant lateral deviation of the saw blade, theprior art system does not react quick enough to prevent damage to thesaw blade and/or the work piece because of the processing time requiredto condition the signals.

[0019] Accordingly, it is an object of this invention to provide a sawcontrol system which is responsive to changing cutting condition so asto optimize saw cutting conditions.

DISCLOSURE OF INVENTION

[0020] These objects are achieved in a control system which continuouslymonitors the lateral displacement of the sawing blade from its designedstraight line position by means of a sensor which is installed at afixed known position relative to the blade. The signal is processed intoan averaged signal proportional relative to a zero reference point, andthus proportional to the lateral motion of the blade for any givenperiod of time. This signal is then compared to a plurality of referencesignals to monitor the lateral position of the blade, and for purposesof adjusting the feed rate at which the material being cut is presentedto the saw. The reference signals are provided in pairs, with the firstbeing those proportional to a predetermined acceptable lateral motionrange, followed by a first, second and third range reference signals.Since every sawing application is different, the set points for thereference levels are empirically determined for the particularapplication.

[0021] The work feed motor has a variable feed rate capability. Anempirically determined table assigns to each depth of cut a thicknessdesignation and an initial entry feed rate assignment. These entry feedrate assignments are either determined empirically or derived fromexisting tables published for most particular saw blade configurations.The greater the depth of cut, the slower the initial entry feed ratewill be. Also provided are a plurality of increasing and decreasing feedrate steps for each initial entry feed rate. These steps can be fixed orpercentage based so that the greater the depth of cut, the less the feedrate step increases, and the smaller the depth of cut, the greater theincreases and decreases.

[0022] Prior to the material being cut being presented to the saw blade,it is first passed through a depth of cut thickness measurement device,where the thickness is measured and compared to the entry feed ratetable and the appropriate initial entry feed rate is selected.

[0023] As the material engages the saw blade, the lateral position ofthe saw blade is continuously monitored by a sensor and compared to theacceptable lateral motion reference signals. If the blade motion signalremains within the acceptable lateral motion signals for a predeterminedperiod of time, then the output to the work feed motor will be increasedone step. This sequence of events will continue as long as the lateralposition of the saw blade remains within the acceptable lateral motionrange.

[0024] If the lateral position of the saw blade moves outside of theacceptable lateral range, but not above or below the first referencepoint, then the increase in feed rate steps will stop. If the lateralposition of the saw blade moves beyond the first reference range, thecontroller will signal the work feed motor to drop its operating speedone step. If the lateral position of the saw blade remains outside ofthe first reference range for a specified period of time after droppinga speed step, the controller will signal the work feed motor to continuedropping steps until the lateral saw blade motion drops within theacceptable lateral motion range.

[0025] If the raw wave signal from the sensor indicates that the lateralmotion of the second reference point range, the feed rate signal fromthe controller will automatically drop a predetermined number of steps,depending upon a preselected set point parameter.

[0026] If the raw wave signal from the sensor indicates that the sawblade has moved laterally past a third reference point, then thecontroller will signal the work feed motor to immediately drop in feedrate to a slow speed to the depth of cut being sawn.

[0027] In a like manner, the controller can be used to step up or downthe blade drive motor and thus provide adjustments for tip speed for theblade.

[0028] The position of the saw blade is also monitored, using thesensor. During those periods of time when the saw blade is not cutting,these readings are used to periodically reset the initial zero referencepoint so as to compensate for changes in position resulting from wear onthe saw and guide blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a sectional side view of a typical prior art band sawblade;

[0030]FIG. 2 is a sectional top view of the band saw blade taken alongplane 2-2;

[0031]FIG. 3 is a schematic representation of a typical band saw showingthe sensor position;

[0032]FIG. 4 is a schematic representation of a typical circular sawblade configuration showing motion sensor position;

[0033]FIG. 5 is a schematic representation of a lateral motion, raw wavesignal for a band saw blade when not engaged in cutting;

[0034]FIG. 6 is a schematic representation of a lateral motion raw wavesignal for a band saw engaged in cutting;

[0035]FIG. 7 is a schematic representational block diagram of thecontrol system;

[0036]FIG. 8 is a schematic representation of the acceptable band width,and the first, second and third reference signals.

BEST MODE FOR CARRYING OUT INVENTION

[0037] It is an object of the present invention to optimize productionof cutting products. To do this, it is necessary to understand thesawblade cutting process and to adjust sawblade rim speed and/or feedspeed to ensure that optimal straight light cuts are achieved at thefastest possible rate. Reference is made to prior art FIGS. 1 and 2.Prior art FIG. 1 discloses a section of a band saw cutting blade 30which is formed of body 32 and teeth 34. The dynamics of band sawcutting will be described in this preferred embodiment in the context ofa band saw cutting dimensional lumber from a log or cant. However, itshould be understood that the dynamics of cutting with other materialsare essentially the same, as are the dynamics of cutting with a radialsaw, as opposed to a band saw. The processes in the control systemdescribed herein apply equally well to the cutting of other materials,including metal, polymers, rods, silicates, and virtually any materialwhich is capable of being cut.

[0038] Again, referring to prior art FIGS. 1 and 2, ideally, as thematerial is being fed into the cutting teeth of the band saw, tips 42 ofteeth 34 chip away at the material being fed into it, with the chips,which in this example are wood chips, or sawdust, collecting in thegullet 36 which is the area defined between adjacent teeth 34. Foroptimal cutting, the teeth 34 and gullet 36 should clear or exit thematerial being cut just as the gullets are nearing completely full. Ifthe material to be cut is fed too slowly, the gullets 36 will remainpartially empty, and the saw is capable of cutting or biting into thematerial at greater distance during its pass through the material as itis being cut. If the material to be cut is being fed in too fast,gullets 36 will fill before the adjoining teeth exit the material and,as a result, the chipped material or sawdust will be forced out alongside body 32 of band saw blade 30.

[0039] Although there are a number of different designs for band saw andcircular saw blades, the typical band saw blade used in cuttingdimensional lumber has, as shown in prior art FIG. 2, has swaged teethwith swaged tips 38, thus forming a wider tip at 38 than the body 32 ofthe blade. The width of the cut is called the kerf, and is shown as 40in the prior art FIG. 2. The purpose of this is to reduce abrasion ofbody 32 as it passes through the material being cut. If the materialfeed rate into the blade is too high, and gullets 36 fill, this excessmaterial will be pushed out along side body 32 and cause rapid andunacceptable wear and heat deformation. Also, if the gullets fill tooearly and material is forced out from the gullets, it may be forced outalong one side of the blade and not the other, thus causing the body 32of blade 30 to become angled within the kerf 40, and thereby cause adeviation from a straight line cut.

[0040] Thus, the two primary factors which must be optimized in order tooptimize the cutting process are the speed of the blade and the rate atwhich material is fed into it.

[0041] These factors are strongly influenced by the conditions andoverall dimensions of the material being cut. For example, a typicalband saw may be used to cut a typical log which is, at its base is 18″in diameter, and at its opposite end, only 12″ in diameter. The same logmay be much denser at its base than at its opposite end, dryer at oneend or the other, or even of a different temperature from one end to theother. The greater the diameter of the log, the greater the depth ofcut, and for a given fixed saw blade tip speed, the log must be fed moreslowly into the blade in order to optimize cutting performance. Yet, ifa constant speed is maintained over the length of the entire log, theslower speed required for optimal cutting at the 18″ base may be muchslower than that which would be permissible for optimal cutting at thesmaller diameter, less dense opposite end.

[0042] Another set of factors which affect optimal cutting speed is thecondition or characteristics of the material being cut. With logs, it isnot uncommon, at the base of the log, to have the grain of the wood andthe sap rings angling out from the center line or longitudinal axis ofthe log. Thus, as the saw blade passes through the log parallel to thelongitudinal axis of the log, it is encountering alternating rings ofwood fiber and sap rings and, as a result, varying densities of materialto be cut. This can result in unequal forces on the swage tips 38, whichcan again displace the blade from its straight-line path, and cause anangled or non-straight cut.

[0043] In a like manner, when the saw blade encounters knots in the log,the same conditions can occur which cause the blade to deviate from itsstraight-line path.

[0044] Ultimately it is the displacement of the blade from its straightline position which results in the non-straight cuts and, for thatreason, in the present invention and as discussed in this preferredembodiment, it is the detecting of the lateral displacement of the bladefrom its designed straight line position which indicates that optimalcutting conditions no longer exist.

[0045] In the preferred embodiment, as shown in FIG. 3, saw blade 30 forband saw 44 is stretched around two opposing band saw wheels 46, andtensioned and guided, in the cutting area, by means of upper and lowerguide blocks 48 and 50. A sensor, 12, as used in the preferredembodiment is an electromagnetic proximity sensor which senses eddycurrent, and thus the distance of a sensor to a metallic object. Thesensor 12 is used to detect the lateral position of band saw blade 30.The initial measurement of the lateral position of the band saw blade 30is used for establishing a zero reference point. This initialmeasurement by the sensor 12 and the control unit 16 provide a means forgenerating an initial lateral position proportional to the initialposition of the saw blade. Subsequent measurements of the lateralposition of the band saw blade 30 are used to detect lateral movement ofthe saw blade away from the zero reference point when the saw blade iscutting material being fed into the saw blade. Thus the sensor serves asthe means for detecting lateral movement of the saw blade away from thezero reference point and also serves as the means of establishing thezero reference point. In the preferred embodiment, sensor 12 is anelectromagnetic proximity sensor developing a 50 MH RF envelope which isaffected by the proximity of a moving metal blade. This proximity sensor12 can thus generate a signal proportional to the detected lateralmovement of the saw blade, and thus indicates the lateral position ofblade 30 relative to itself. This serves as a means for generating asignal proportional to the detected lateral movement of the saw blade,and also a means for generating a blade motion signal proportional tothe average detected lateral movement of the saw blade of a preselectedperiod of time. Sensor 12 is installed in a fixed, known position and isattached to the sawing machine frame and/or foundation. In the preferredembodiment, sensor 12 can be attached to either of guide blocks 48 or50, with the preferred attachment attached to the bottom of the upperguide block which is in a position over the top of the material beingcut. An alternate position is attached to either side of the lower guideblock 50. In some cases, when the distance between the guide blocks 48and 50 is more than 4 times the width of the band saw blade, having botha top and a bottom sensing means is desirable. The sensor 12 may also beaffixed so that the distance below the guide block between the work andthe edge of the saw guide produces a number that represent a one to fivetimes multiple of the sensed sawblade lateral position within the workbeing sawn. This ratio is the relationship between the sensing meansmovement and the actual movement of the saw within the work. In thepreferred mounting, this requires that the top saw guide block 48 bepositioned far enough above the work so that the sensor 12 obtainssuperior representation of sawblade lateral movement within the work.The sensor means must be mounted so it senses the movement closest tothe saw teeth or just behind the gullets. In case of a double-cutmachine, a sensor is used for both front and back of the saw blade.

[0046] In a circle saw machine application, such as that shown in FIG.4, the sensor 12 is attached to the machine frame, preferably in aradial location equidistant from the entrance and exit of and adjacentto circular saw blade 52. Sensor 12 is also placed, as with the band sawmachine, not more than one diameter of the sensor behind the gullets ofthe blade.

[0047] When band saw 44 is operating, and not cutting, there maytypically be a small amount of lateral movement of the blade from itszero reference or stationary position. This typically will be asinusoidal type of oscillation of minimal measurement, and is shown inrepresentational format in FIG. 5. When the band saw is actually cuttingmaterial, its lateral displacement and oscillations are considerablymore complex due to the various factors discussed above. The raw wavesignal, from sensor 12, would correspond, during cutting conditions, toa path more or less similar to representational cutting lateraldisplacement path 62, as shown in FIG. 6. This raw wave signal is sentfrom sensor 12 to primary signal conditioning means 14 as shown in FIG.7, in which a proportional electrical signal representing the referenceposition of the saw blade is generated. The primary signal conditioningmeans 14 thus establishes a reference signal proportional to theproportional signal generated by the sensor 12. This serves as a meansfor establishing a reference signal, which can be a first referencesignal of several, to the proportional signal generated at a preselectedacceptable lateral movement of the saw blade. The reference signalindicates a preselected accepted lateral movement of the saw blade 52,and the signal sent from sensor 12 is compared to it, providing a meansfor comparing the generated signal to the reference signal. This primarysignal conditioning means 14 can be incorporated into either sensor 12or incorporated within the control unit 16. The configuration may changeto accommodate advances in technology without changing the function orlogic of the invention. This signal can now be used for direct feed ratelogic control and further mathematically calculated into mean or averageposition and peak-to-peak vibration, and RMS values for additionalcontrol. These separate signals, reduced to engineering units ofmeasurement, are now ready to be used in the control logic.

[0048] In the preferred embodiment, the signal conditioning means 14 isused to average the raw signal being sent by sensor 12. There are, inthis preferred embodiment, two averagings occurring, the first being theaverage lateral displacement absolute valves in both the plus and minusdirections from the zero reference point, and second, an averaging overtime of the continuous signals being received from sensor 12. In thepreferred embodiment, the time averaging occurs between ten millisecondsto two hundred milliseconds, depending upon the application. The purposeis to avoid having the control system react to non-harmful transients,such as for example, the blade encountering a small knot in the log.

[0049] The control unit 16 can incorporate means such as a centralprocessing unit, computer, microprocessor or other programmable logiccontroller. The operator access unit 18 allows the operator to examineand change control parameters and set points.

[0050] The control unit 16 contains several pairs of control set points.Each of these control set points correspond to a reference signal, andthe control unit 16 compares the generated signal to the referencesignal. If the generated signal is less than the reference signal, thenincreasing the feed rate is initiated. If the generated signal isgreater than the reference signal, then decreasing the feed rate isinitiated. The control unit thus serves as the means for comparing thegenerated signal to the reference signal. As shown in FIG. 8, these setpoints are on either side of the zero reference or center position,having both a positive and a negative setting. The first set points arelabeled the range of acceptable lateral motion and correspond to a firstreference signal, which is proportional to the blade motion signalgenerated at a preselected acceptable lateral movement of the saw blade.The next set points are labeled the first level of unacceptable lateralmovement, and is the +1 and −1 range. The next set points are the secondlevel of unacceptable lateral movements, and is the +2 and −2 range,followed by the third level of unacceptable lateral movement, the +3 and−3 range. Additional ranges can be added as necessary. Every sawingapplication is different and requires set points to be set at differentlevels. For example, the +3 or −3 level can be ten to twenty timesgreater than the acceptable lateral motion level.

[0051] The work feed motor 20 has variable feed rate capabilities. Anempirically determined table assigns to each depth of cut, a thicknessdesignation and an initial entry feed rate assignment. These entry feedrate assignments are either determined and set empirically or derivedfrom existing tables published for most particular saw bladeconfigurations. The greater the depth of cut, the slower the initialentry feed rate will be. Along with the entry feed rate, there areprovided a plurality, which in the preferred embodiment is four or more,of increasing feed rate steps and four or more decreasing feed ratesteps. These steps can be fixed or percentage based, so that the greaterthe depth of cut, the less the feed rate step increases, and the smallerthe depth of cut, the larger the step increases.

[0052] In a depth of cut feed rate sawing machine application, thenormal continuous sequence of events for the controller system is asfollows:

[0053] The work, which in this description of the Best Mode is a log 28,passes through a depth of cut thickness measurement means 70 prior tofeed entry into the saw blade so that its thickness is measured andcompared to a predetermined entry feed rate table and the appropriateoutput value is sent to the work feed motor 20 to move the log or intothe saw blade at the appropriate predetermined speed. The depth of cutor thickness measurement means 70 is typically a set of optical sensors,or other devices, all of which are well known in the art.

[0054] As log 28 engages saw blade 30, the lateral position of saw blade30 is continuously sensed by sensor 12 and compared to the referencesignals identified as the acceptable lateral motion signals in FIG. 8.These reference signals are proportional to the blade motion signal thatwould be generated at predetermined acceptable lateral movement of thesaw blade.

[0055] The averaged blade-motion signal is then compared in the controlunit 16 to the zero reference signal and the acceptable lateral motionor first reference signals. If the blade motion signal remains withinthe acceptable lateral motion reference signals (the first referencesignal) for a period of time, for example, twenty-five milliseconds orone hundred fifty milliseconds, then the output to the work feed motor20 will be increased one increment. This loop continues at specifiedtime intervals as long as the lateral position of the saw blade, asindicated by the generated blade motion signal, is in the acceptablelateral motion range, until the highest feed rate step for this depth ofcut is reached.

[0056] If the lateral position of the saw blade, as indicated by thegenerated blade motion signal, moves outside of the acceptable lateralmotion range, but not above or below the +1 or −1 or first referencepoint range, the increase in feed rate steps will stop. As long as thelateral position of the saw blade remains between the acceptable lateralmotion and the +1 or −1 range, the feed rate remains at its obtainedsetting.

[0057] If the lateral position of the saw blade, as indicated by thegenerated blade motion signal, crosses beyond either the +1 or −1 orsecond reference point range, the first level of unacceptable lateralmovement, the control unit 16 will send a signal to the work feed motor20 to decrease the feed rate one increment. If the lateral positionremains outside of the +1 or −1 range for a specified period of time,for example, one hundred milliseconds, the controller 16 will signal thework feed motor 24 to drop another step. This process will continueuntil lateral saw blade motion drops within the acceptable lateralmotion range again.

[0058] If the lateral position, as indicated by the generatedproportional blade motion signal, crosses into the +2 or −2 or thirdreference signal range (the second level of unacceptable lateralmovement of the saw blade), the feed rate signal from the controllerwill automatically drop one, two or three steps, depending upon thepreselected set point parameter. This system provides a means forcomparing the blade motion to the first and second reference signals.

[0059] The primary signal conditioning means 14 also monitors andmaintains the raw wave signal being provided from sensor 12, withoutaveraging over time, but rather in a peak-to-peak absolute valueconfiguration. If, in the preferred embodiment, the raw wave signalpasses over the value of the fourth plus or minus reference signals (thethird level of unacceptable lateral movement), then controller 16 willsignal the work feed motor 24 an immediate drop in feed rate to theslowest speed for the depth of cut being sawn. In this manner, the speedsteps can only cycle up one at a time, but can move from the top step tothe lowest step in one jump if the raw wave signal exceeds the thirdreference value. This is done as a safety precaution, since the rawsignal can be processed much quicker than the time averaged blade motionsignal.

[0060] In this manner, the control system operates within theestablished set points to cycle the feed speed steps up or downaccording to the lateral position of the saw blade. These steps changethe control feed rate both above and below the entry rate, including areturn to the entry rate as one of the steps.

[0061] In a like manner, control unit 16 can be used to step up or downsaw blade drive motor 24 and thus provide adjustment for the tip speedfor blade 30.

[0062] Another control consideration, depending upon the application, isthe optional monitoring of both the work feed motor load monitor 22 andsaw blade motor load monitor 26 to monitor load amps or horsepowerusage. Set points for maximum amps can then be used to either inhibitfeed rate increases or drop the feed rate one step, and in a like mannerinhibit or increase blade speed one step. If a chipper or slabber isutilized in series with the saw blade assembly, a load measurement meanscan also be provided to control the speed rate steps of these machinesin the same manner as the saw blade and feed rate motors.

[0063] As normal wear occurs on band saw 44 and upper and lower guideblocks 48 and 50, the distance between sensor 12 and band saw blade 30can change. This wear can easily amount to as much as ten thousandths ofan inch per hour. This type of wear can alter the position of the zeroreference set point, and, in many applications, can drastically affectthe effectiveness of the calibrations of the first, second and thirdreference points. To automatically compensate for this wear, the zeroreference point is periodically recalibrated, and thus the values of theacceptable lateral motion, first, second and third levels ofunacceptable lateral movement are updated. This is accomplished bymonitoring the position of the saw blade, using sensor 12, and controlunit 16 during those time periods when material is not being fed intothe saw and the saw is not cutting. The sensor 12 thus provides a meansfor detecting the location of the saw blade when it is not engaged insawing material to establish an initial zero reference point. At thebeginning of the work cycle, this first detection of location of the sawblade, when not engaged in sawing material, is used to establish theinitial zero reference point. Thereafter, in the preferred embodiment,each time the saw is not working or engaged in sawing material, itslocation is monitored by sensor 12 and saved in control unit 16. Thesensor 12 and the control unit 16 thus serve as a means for detecting anupdated location and generating an updated lateral position signalproportional to the position of the saw blade when it is not engaged insawing material. Averages of the stored readings are then taken, in thepreferred embodiment, every five minutes. This average is then comparedwith the readings of the then current zero reference value, and ifdifferent, the zero reference value is reset as needed. Thus, sensor 12and control unit 16 also provide a means of resetting the zero referencepoint to conform to the updated lateral position signal.

[0064] The next set points the +1 or −1 range, and corresponds to asecond reference signal, which again is proportional to the blade motionsignal generated at a first level of unacceptable lateral movement ofthe saw blade. The sensor thus provides a means for generating a secondreference signal proportional to the blade motion signal generated at afirst level of unacceptable lateral movement of the saw blade. The nextset points +2 and −2 range, followed by the +3 and −3 range, establish athird reference signal and a fourth reference signal, each proportionalto the blade motion signal generated at a second and third level ofunacceptable lateral movement of the saw blade. The sensor 12 thusserves as a means of generating a third and a fourth reference signalproportional to the blade motion signal generated at a second and thirdlevel of unacceptable lateral movement of the saw blade. Comparing thesesignals in the control unit 16 provides a means of comparing the blademotion signal to the third reference signal, and if the blade motionsignal is greater than the third reference signal, then decreasing thefeed rate at least two increments. The sensor 12 also provides a meansfor comparing a fourth reference signal proportional to the blade motionsignal generated at a third higher level of unacceptable lateralmovement of the saw blade. The control unit 16 also provides a means forcomparing the actual detected lateral movement of the saw blade awayfrom the zero reference point to the fourth reference signal, and ifgreater than the fourth and if greater than the fourth reference signal,then decreasing the feed rate to the lowest available feed rate for thematerial being cut.

[0065] A second preferred embodiment of the invention utilizes the samesensing and adjusting system as described above, but rather thanadjusting the feed rate of the work piece, adjust the rim speed of thesaw blade which is operating with this system. In all other respects,this embodiment uses the same sensing, averaging, comparison, signalgenerating, and reference signal generating components as the systemdescribed above. The sensor 12 and control unit 16 provide the means forestablishing the zero reference point, the means for detecting thelateral movement of the saw blade, the means of generating a signalproportional to the detected lateral movement of the saw blade, themeans for establishing a signal proportional to the proportional signalgenerated at a preselected acceptable lateral movement of the saw blade,and the means for comparing the generated signal to the referencesignal, and if the generated signal is less than the reference signal,than increasing the rim speed, and if the generated signal is greaterthan the reference signal, then decreasing the rim speed.

[0066] While there is shown and described the present preferredembodiment of the invention, it is to be distinctly understood that thisinvention is not limited thereto but may be variously embodied topractice within the scope of the following claims.

I claim:
 1. An apparatus for computer control of feed rate of materialto be cut by a saw having a saw blade and a wearable guide block whichcomprises: means for establishing a zero reference point for a lateralposition of the saw blade by determining the saw blade position whenmaterial is not being sawed; means for detecting lateral movement of thesaw blade away from the zero reference point when the saw blade iscutting material being fed into the saw blade; means for generating asignal proportional to the detected lateral movement of the saw blade;means for establishing a reference signal proportional to theproportional signal generated at a preselected acceptable lateralmovement of the saw blade; means for comparing the generated signal tothe reference signal, and if the generated signal is less than thereference signal, then increasing the feed rate, and if the generatedsignal is greater than the reference signal, then decreasing the feedrate; and means for automatically and periodically reestablishing a zeroreference point to compensate for guide block wear.
 2. The apparatus ofclaim 1 in which said means for detecting lateral movement of said sawblade is proximity sensor positioned adjacent to said saw blade forgenerating a signal related to the position of said saw blade relativeto said proximity sensor.
 3. The apparatus of claim 1 in which saidmeans for reestablishing said zero reference point to compensate forguide block guide wear further comprises means for determining theposition of the saw blade when not sawing material to reestablish thezero reference position.
 4. The apparatus of claim 1 wherein said meansfor automatically and periodically reestablishing a zero reference pointto compensate for guide block wear further comprises: means for samplingsaid proportional signal generated by said proximity sensor when saidsaw blade is not sawing material; and means for periodically averagingtwo or more of said samples of said proportional signal generated bysaid proximity sensor to reestablish said zero reference point.
 5. Anapparatus for controlling a feed rate of material to be cut by a sawhaving a saw blade and a wearable guide block which comprises: means forestablishing a zero reference point for a lateral position of the sawblade by determining the saw blade position prior to sawing material;means for detecting lateral movement of the saw blade away from the zeroreference point when the saw blade is cutting material; means forgenerating a blade motion signal proportional to the detected lateralmovement of the saw blade; means for establishing a first referencesignal proportional to the blade motion signal generated at apreselected acceptable lateral movement of the saw blade; means forgenerating a second reference signal proportional to the blade motionsignal generated at a first level of unacceptable lateral movement ofthe saw blade; means for comparing the blade motion signal to the firstand second reference signals, and if the blade motion signal is lessthan the first reference signal, then increasing the feed rate, and ifthe blade motion signal is greater than the first reference signal andless than the second reference signal, then neither increasing ordecreasing the feed rate, and if the blade motion signal is greater thanthe second reference signal, then decreasing the feed rate; and meansfor automatically and periodically reestablishing said zero referencepoint to compensate for guide block wear.
 6. The apparatus of claim 5 inwhich said means for detecting lateral movement of said saw blade isproximity sensor positioned adjacent to said saw blade for generating asignal related to the position of said saw blade relative to saidproximity sensor.
 7. The apparatus of claim 5 in which said means forreestablishing said zero reference point to compensate for guide blockguide wear further comprises means for determining the position of thesaw blade when not sawing material to reestablish the zero referenceposition.
 8. The apparatus of claim 5 wherein said means forautomatically and periodically reestablishing a zero reference point tocompensate for guide block wear further comprises: means for samplingsaid proportional signal generated by said proximity sensor when saidsaw blade is not sawing material; and means for periodically averagingtwo or more of said samples of said proportional signal generated bysaid proximity sensor to reestablish said zero reference point.
 9. Theapparatus of claim 5 which further comprises: means for generating athird reference signal proportional to the blade motion signal generatedat a second, greater level of unacceptable lateral movement of the sawblade than that of said second reference signal; and means for comparingthe blade motion signal to the third reference signal, and if the blademotion signal is greater than the third reference signal, thendecreasing the feed rate.
 10. The apparatus of claim 9 which furthercomprises: means for generating a fourth reference signal proportionalto the blade motion signal generated at a third higher level ofunacceptable lateral movement of the saw blade; means for comparing theactual detected lateral movement of the saw blade away from the zeroreference point to the fourth reference signal, and if greater than thefourth reference signal, then decreasing the feed rate to the lowestavailable feed rate for the material being cut.
 11. An apparatus forincrementally controlling a feed rate of material to be cut by a sawblade which comprises: means for establishing a zero reference point fora lateral position of the saw blade by determining the saw bladeposition when the saw blade is not sawing material; means for detectinglateral movement of the saw blade away from the zero reference pointwhen the saw blade is cutting material; means for generating a blademotion signal proportional to the detected lateral movement of the sawblade; means for establishing a first reference signal proportional tothe blade motion signal generated at a preselected acceptable lateralmovement of the saw blade; means for generating a second referencesignal proportional to the blade motion signal generated at a firstlevel of unacceptable lateral movement of the saw blade; means forcomparing the blade motion signal to the first and second referencesignals, and if the blade motion signal is less than the first referencesignal, then increasing the feed rate one increment, and if the blademotion signal is greater than the first reference signal and less thanthe second reference signal, then neither increasing or decreasing thefeed rate, and if the blade motion signal is greater than the secondreference signal, then decreasing the feed rate one increment; and meansfor periodically reestablishing said zero reference point to compensatefor guide block wear.
 12. The apparatus of claim 11 in which said meansfor reestablishing said zero reference point is configured toautomatically reestablish said zero reference point.
 13. The apparatusof claim 11 in which said means for reestablishing said zero referencepoint to compensate for guide block guide wear further comprises meansfor determining the position of the saw blade when not sawing material,and resetting the zero reference position.
 14. The apparatus of claim 11wherein said means for automatically and periodically reestablishing azero reference point to compensate for guide block wear furthercomprises: means for sampling said proportional signal generated by saidproximity sensor when said saw blade is not sawing material; and meansfor periodically averaging two or more of said samples of saidproportional signal generated by said proximity sensor to reestablishsaid zero reference point.
 15. The apparatus of claim 11 which furthercomprises: means for generating a third reference signal proportional tothe blade motion signal generated at a second, greater level ofunacceptable lateral movement of the saw blade than that of said secondreference signal; and means for comparing the blade motion signal to thethird reference signal, and if the blade motion signal is greater thanthe third reference signal, then decreasing the feed rate.
 16. Theapparatus of claim 11 which further comprises: means for generating afourth reference signal proportional to the blade motion signalgenerated at a third higher level of unacceptable lateral movement ofthe saw blade; means for comparing the actual detected lateral movementof the saw blade away from the zero reference point to the fourthreference signal, and if greater than the fourth reference signal, thendecreasing the feed rate to the lowest available feed rate for thematerial being cut.
 17. An apparatus for incrementally controlling afeed rate of material to be cut by a saw having a saw blade and awearable guide block which comprises: means for establishing a zeroreference point for a lateral position of the saw blade by determiningthe position of the saw blade when it is not sawing material; means fordetecting lateral movement of the saw blade away from the zero referencepoint when the saw blade is cutting material being fed into the sawblade; means for generating a blade motion signal proportional to theaverage detected lateral movement of the saw blade over a preselectedperiod of time; means for establishing a first reference signalproportional to the blade motion signal generated at a preselectedacceptable lateral movement of the saw blade; means for generating asecond reference signal proportional to the blade motion signalgenerated at a first level of unacceptable lateral movement of the sawblade; means for comparing the blade motion signal to the first andsecond reference signals, and if the blade motion signal is less thanthe first reference signal, then increasing the feed rate one increment,and if the blade motion signal is greater than the second referencesignal, then decreasing the feed rate one increment, and if the blademotion signal is greater than the first reference signal and less thanthe second reference, stopping the increase in feed rate; and means forperiodically reestablishing said zero reference point to compensate forguide block wear.
 18. The apparatus of claim 17 in which said means forreestablishing said zero reference point is configured to automaticallyreestablish said zero reference point.
 19. The apparatus of claim 17 inwhich said means for reestablishing said zero reference point tocompensate for guide block guide wear further comprises means for is bydetermining the position of the saw blade when not sawing material, andresetting the zero reference position.
 20. The apparatus of claim 17which further comprises: means for generating a third reference signalproportional to the blade motion signal generated at a second, greater,level of unacceptable lateral movement of the saw blade than that of thesecond reference signal; means for comparing the blade motion signal tothe third reference signal, and if the blade motion signal is greaterthan the third reference signal, then decreasing the feed rate.
 21. Theapparatus of claim 17 which further comprises: means for generating afourth reference signal proportional to the blade motion signalgenerated at a third higher level of unacceptable lateral movement ofthe saw blade; means for comparing the actual detected lateral movementof the saw blade away from the zero reference point to the fourthreference signal, and if greater than the fourth reference signal, thendecreasing the feed rate to the lowest available feed rate for thematerial being cut.
 22. The apparatus of claim 17 wherein the means forestablishing a zero reference point for the lateral position of the sawblade further comprises: means for detecting the location of the sawblade when it is not engaged in sawing material to establish an initialzero reference point; means for generating an initial lateral positionproportional to the initial position of the saw blade; means for againdetecting an updated location of the saw blade when it is not engaged insawing material; means for storing one or more updated locations of thesaw blade when it is not engaged in sawing material; means forperiodically averaging the updated saw blade locations; means forgenerating an updated lateral position signal proportional to theaveraged position of the saw blade when not engaged in work; and meansfor resetting the zero reference point to conform to the updated lateralposition signal.